Abstract

An improved experimental setup and data evaluation procedure are presented for a Loschmidt cell combined with interferometry to measure concentration-dependent binary diffusion coefficients. We overcome long-standing discrepancies about the concentration dependence found in the literature. The systematic analysis of the residuals from parameter estimation enabled the improvement of the experimental setup and the identification of relevant fitting parameters. In particular, we found that it is crucial to account for uncertainties (1) in the initial conditions, (2) in the thermal stability of the optical setup, and (3) in camera calibration. The improved experimental setup and data evaluation procedure are validated with diffusion measurements of the system helium-krypton. The concentration dependence of the diffusion coefficient is successfully determined from multiple experiments with gas mixtures of various initial compositions in the half-cells of the Loschmidt cell. The agreement with literature data and the excellent quality of fit allow for high confidence in the results. In PartII of this paper (Wolff et al., in Int J Thermophys, 2018, 10.1007/s10765-018-2451-7), the improved measurement setup is combined with a refined diffusion model to determine concentration-dependent diffusion coefficients from single measurements of mixing pure gases.